1. Field of the Invention
The present invention relates to a novel method of ink jet recording and an ink jet recording apparatus that are capable of forming full-color images which are free from the occurrence of pseudo-contours and are higher in picture quality.
2 Description of the Related Art
A method of ink jet recording is used to record an image or the like by discharging droplets of ink from nozzles of a recording head by causing these droplets of ink to be absorbed by a recording material such as paper or cloth. The amount of noise generated according to this method is small, and no particular fixing treatment is required, and it is capable of effecting high-speed recording and full-color recording.
The full-color recording is effected by subjecting the three colors of yellow (Y), magenta (M), and cyan (C), or four colors with black (K) added thereto to subtractive mixing of colors. Namely, full-color recording is effected by discharging the three colored inks or four colored inks with black (K) added thereto from nozzles used exclusively for the respective colors of the recording head while the respective amounts of the colored inks to be discharged are being controlled, and by allowing the respective inks to be mixed and absorbed by each picture element of the recording material.
For instance, in a conventional printer in which cylindrical piezoelectric elements are used in a printer head of an ink jet system, the gradations of density can be expressed by changing the diameter of the dots to be printed on the recording sheet.
Meanwhile, since the ratio of change between a maximum dot and a minimum dot is not very large, there are cases where areas having a sufficient density are lacking to output a natural color image. Accordingly, a low-density ink and a high-density ink both of the same color are prepared for each color, and the high- and low-density inks are selectively used by changing over the heads in accordance with the high- and low-density areas, thereby securing areas having necessary densities, as disclosed in, for example, U. S. Pat. Nos. 4,551,736, 4,533,920, 4,533,923, and 4,695,846.
However, a problem has newly arisen in that differences in color emerge as between cases where a low-density ink and an ink of another color are discharged to a specific position on the recording paper and cases where a high-density ink of the same color as that of the low-density ink and an ink of another color are discharged thereto.
In other words, if the high- and low-density inks are changed over when a color is changing smoothly in an output image, pseudo-contours occur in that changed-over portion, with the result that the image becomes disadvantageously unnatural.